1. Field of the Invention
The present invention relates to amplifier circuits such as power amplifiers adapted to audio devices.
The present application claims priority on Japanese Patent Application No. 2009-79463, the content of which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, amplifier circuits have been used to drive electric loads (e.g. speakers) in response to input signals (e.g. audio signals). When the level of an input signal exceeds a predetermined range of amplitude, an amplifier circuit is subjected to clipping with respect to the waveform of an output signal. Upon receipt of an output signal having a clipped level from an amplifier circuit, a speaker (serving as an electric load) may produce an artificially-distorted and offensive sound. For this reason, it is necessary to prevent clipping from occurring in waveforms of amplified signals.
Various types of amplifier circuits employing clipping prevention measures have been developed and disclosed in various documents.    Patent Document 1: Japanese Patent Application Publication No. 2007-124624    Patent Document 2: Japanese Patent Application Publication No. 2007-124625
Conventionally, amplifier circuits employing clipping prevention measures haven been designed to adjust the level of an input signal before forming an output signal or to appropriately adjust an amplification factor. For example, Patent Document 1 employs interrupted attenuation of an input signal, and Patent Document 2 employs a gain controller for decreasing a gain of amplification.
However, the above measures bring a decline in the level of an output signal of an amplifier circuit, thus causing a speaker to produce a deficient sound lacking power and dynamics.